Tellymate is an Arduino shield that outputs all Serial.print() commands to a television (NTSC or PAL composite video). I’ve had one kicking around for a couple of years now. I bought it thinking that I’d like to build a “new” kind of interface/display. I even bought an inexpensive portable TV/DVD player for the purpose. That project is still on my ‘to-do’ list, but I had another problem—that Tellymate solved simply and elegantly.

I’ve been picking at the Media Circus project for about year, making improvements, letting it run to see if any bugs cropped up. Media Circus is a scrolling marquee that displays amusing headline news mashups. It receives updates from Twitter once a day, early in the morning. To do this, it needs to self-reset. This is not simply a matter of running a wire from a digital output pin to the Reset pin on the Arduino. A dependable self-reset requires a delay and ‘safety switch’ circuit.

The Problem…

Because the unit resets only once a day, I needed several days to test it. It seemed to work as designed with more frequent resets using a test program, but when I incorporated my reset code into the Media Circus sketch and let it run, I discovered that it would reset the first time, but never again. I needed to know what was going on in the program. Using the Arduino IDE, if you want Arduino to tell you what state it’s in at various points, you drop in Serial.print() statements and then open Arduino’s Serial Monitor. For short runs, this works, but Serial Monitor sometimes crashes if you give it lots of data to display over a long period of time. Additionally, when the system resets, it closes the Serial Monitor.

My next thought was to bypass Serial Monitor and attach a small LCD screen to show the various values. I tried the Arduino built-in LiquidCrystal library, but it didn’t work for me with the particular arrangement of hardware and software—I wasn’t able to figure out precisely why. Next, I tried a different library, arduinoshiftreglcd, which worked with the MEGA and the Ethernet Shield, but failed when in the presence of the Ethernet or EthernetUDP libraries. I was about to look at the New LiquidCrystal library, when I remembered the Tellymate.

The Solution…

Tellymate doesn’t require any additional code: if you can print to the Serial Monitor, it will show up on the TV. But there are two very simple functions that Batsocks provides that were useful to me: screen_clear and cursor_move. My TV display shows the number of seconds since midnight, the rough geographic location (Beijing/Moscow/London/Halifax/Vancouver) and Daylight Savings Time/Standard Time, and the epoch time at reset. This has finally allowed me to find—and solve—the problem!

And now, for today’s headline (June 8, 2012):

Small plane crashes on who’s giving it all away

You can look at the other headlines that are running on Media Circus, or follow General Eccentric.